Remove the support of fallback from DTLS to SDES.

webrtc/p2p/base/jseptransport.cc

Index: webrtc/p2p/base/jseptransport.cc
diff --git a/webrtc/p2p/base/jseptransport.cc b/webrtc/p2p/base/jseptransport.cc
index 191d34fcada0f43f57e0ae509a442401346aa5f7..ac756416e85ee3bbbb5400342abb775a0210881d 100644
--- a/webrtc/p2p/base/jseptransport.cc
+++ b/webrtc/p2p/base/jseptransport.cc
@@ -330,12 +330,7 @@ bool JsepTransport::ApplyLocalTransportDescription(
     std::string* error_desc) {
   dtls_transport->ice_transport()->SetIceParameters(
       local_description_->GetIceParameters());
-  bool ret = true;
-  if (certificate_) {
-    ret = dtls_transport->SetLocalCertificate(certificate_);
-    RTC_DCHECK(ret);
-  }
-  return ret;
+  return true;
 }
 
 bool JsepTransport::ApplyRemoteTransportDescription(